1. Field of the Invention
The present invention relates to a diesel particulate filter apparatus.
2. Description of the Related Art
Conventionally, as a diesel particulate filter apparatus (hereinafter referred to as “DPF apparatus”), there is an apparatus in which a diesel particulate filter (hereinafter referred to as “DPF”) made of ceramics is held in a container to which an exhaust gas inlet pipe connected to an exhaust gas passage of a diesel engine, and an exhaust gas outlet pipe connected to the downstream side are attached. Exhaust gas which flows into the apparatus through the exhaust gas inlet pipe is passed through a DPF, and is then discharged from the exhaust gas outlet pipe on the downstream side. In such an apparatus, the container has functions of expanding and contracting exhaust gas, and holding the DPF.
In such a DPF apparatus, when soot (diesel particulates) is eccentrically collected in the DPF, the collection performance of the DPF is lowered.
In a regeneration process, when the gas flows ununiformly, the DPF temperature is not even, and hence there is a portion which fails to reach the regeneration temperature.
As a structure for allowing exhaust gas to uniformly flow, there is a diffuser in which the diffusing structure is tapered, or a structure in which a perforated plate having small holes are opened at irregular intervals is disposed in a diffusion chamber.
FIG. 12 shows an example of a diffuser in which the diffusing structure is tapered.
In the DPF apparatus 101, tapered diffusers 103 are disposed in front and rear of a container 102, respectively.
Usually, it is said that, in order to attain an even flow distribution, the diffusers 103 are preferably tapered at 6 degrees so that a gas flow does not separate from a pipe wall.
As shown in FIG. 13, the taper angle must be set small in order to obtain a uniform flow in the diffusers 103. As the expansion ratio of the diameter d1 of an exhaust gas inlet pipe 104 and the diameter d2 of a DPF 105 is larger, the diffusion chamber length L is longer.
When the diffusers 103 are tapered on the basis of the diameter d1 of the exhaust gas inlet pipe 104 and the diameter d2 of the DPF 105, the diffusion chamber length L must be about 1 m. Such a length cannot be practically used.
By contrast, when a perforated plate 108 in which small holes are opened at irregular intervals is disposed in a diffusion chamber 107 as shown in FIGS. 14 and 15, the length of the diffusion chamber can be shortened.
In the configuration where only the perforated plate 108 is employed, because that the amount of exhaust gas of the engine largely changes, there is a problem that in order to equalize the flow rate profile over the whole area (uniformalize the gas flow also in a peripheral portion), the total opening area must be reduced to raise the gas-flow resistance.
The gas flow can be uniformalized also by a three-dimensional structure. However, such a structure requires a complicated design, and hence cannot be practically used.